Commercial plasma sources are used for both deposition onto and etching from surfaces for a wide variety of industrial applications, especially semiconductor, optical, and magnetic thin film processing. The plasma formed by such sources generates reactive neutral and ionic species which can chemically and/or physically interact with surfaces to deposit or remove material.
In many processes, the use of energetic ions from plasma sources can result in the deposition of materials with unique properties or allow the etching of surfaces under conditions which would not otherwise be effective. A method for processing substrates in a plasma can include an ion source mounted in a vacuum chamber in which the substrate is present. A gas with specific chemical properties is supplied to the ion source for ionization. The plasma generated is a mixture of various reactive neutral and ionic chemical species as well as energetic electrons. The energy of the ionic species interacting with the surface depends upon plasma electrical properties and pressure. Typically, the energy of ions bombarding the substrate is controlled by means of the substrate bias. Alternatively, if the substrate is electrically floating, the ion energy will be determined by the electron energy distribution which determines the difference between the plasma potential and the potential at the surface for which there is zero net current (floating potential). Control of ion energy is desirable since deposition or etching process characteristics and resulting material properties often depend strongly on this parameter.
In some applications, it is desirable to process both sides of a substrate simultaneously. This is typical in the deposition of thin layers of various materials in the manufacture of magnetic hard disks used in magnetic memory systems. In this case, ion sources are positioned on opposite sides of the disk. However, ion sources which utilize an anode for establishing a plasma potential tend to exhibit plasma instability and oscillation when two such sources are operated simultaneously in a processing chamber. Such unstable behavior does not permit predictable ion generation and process stability. Also, it has proven difficult to coat thin films with properties which will satisfy the requirements of a protective film on a hard disk, for example, for computer memory applications. Thinner coatings in such a case permit the head to fly closer to the magnetics of the disk as to permit an increase in areal density. In depositing overcoatings, the coating should have sufficient hardness, density, and adhesion as well as practical qualities in the finished disk, including high deposition rates and low numbers of macroscopic particles on the surface. Accordingly, there is a need for improved substrate processing systems and methods wherein ion sources may operate in a stable manner in a processing chamber and wherein the properties of the deposited layers may be improved for their intended purpose.
These same practical requirements set the standards for single sided coating as well. For example if a protective coating is desired for an optical substrate, uses of the disk require that coatings that are deposited be deposited with the desired hardness, density and adhesion at a high rate while extremely thin and that variations through the presence of varying particles be minimized.